海洋細菌に関する研究II : 海洋細菌の特異的無機塩要求性について

This study was undertaken to test the requirement of marine bacteria for inorganic salts, with an attempt to establish a reliable criterion to distinguish true marine bacteria from terrestrial ones. In this paper the author deals with the results of morphological and physiological tests, with special emphasis on the requirement of inorganic salts in sea water, of several hundred strains of aerobic, heterotrophic bacteria isolated from various sources. Of the organisms used in this work, 275 cultures were isolated from sea water in the northern part of the North Pacific and the Bering Sea. In addition 13 cultures isolated from the surface of fishes, 7 strains from the National Collection of Marine Bacteria, 18 strains of Vibrio parahaemolyticus and similar strains, and 37 of other named strains of terrestrial bacteria were employed in the experiments. The results obtained from comparative observations on the mineral requirements of marine and terrestrial bacteria were as follows. 1. These microorganisms showed different mineral requirements. This was demonstrated in experiments with a basal medium which contained only 0.05 percent of polypeptone and 0.01 per cent of yeast extract as organic matter. 2. All the strains were tested for their growth capacity in the following five types of defined media during six days incubation at 25°C. The media (pH 7.8) contained, common to all, 0.05 percent of polypeptone and 0.01 percent of yeast extract, which were dissolved in; (a) pure water , (b) 0.5 percent NaCl solution, (c) 3 percent NaCl solution, (d) Herbst's artificial sea water diluted six-fold, and (e) Herbst's artificial sea water. 3. The results above mentioned tell us that one is able to group the test organisms into three patterns by growth capacity manifested in these media. One of them, which includes terrestrial bacteria, is characterized by the capacity to grow in five types of defined media . Another group lacks the capacity to grow in (a) medium or both (a) and (b) media. The last one, to which the majority of marine isolates belong, is characterized by incapability to grow in the media (a), (b), and (c). Each of the three types were designated as Terrestrial (T-) type, Halophilic (H-) type, and Marine (M-) type bacteria. 4. Terrestrial type bacteria showed a moderate growth without any supplement of inorganic salts to the basal medium and ones who did not take special requirements of mineral salts. Most of them grew best at 0.5 percent of salt concentration, and tolerated some growth in 5 to 7 per cent NaCl . They could grow a t 37 °C.5. Halophilic type bacteria were ones which required to NaCl, but did not require to the other minerals in sea water. They grew best in 3 percent of salt concentration and tolerated some growth at 12 percent NaCl. And about half of were able to grow in 37°C. Their NaCl requirement could be partialy replaced with other salts. In other words, V.parahaemolyticus only requires NaCl, and concerning the V.parahaemolyticus’s growth, NaCl has a function like osmolar control. Marine type bacteria have special requirement for minerals. Not only NaCl but also other minerals such as K-, Mg-, and Ca-salt in sea water are needed for their growth. Most of them were able to grow in the artificial sea water media with a salt concentration ranging from 0.5 to 12 per cent. In the majority of the strains, the salt concentration optimum for growth was found to be 3 to 7 per cent. But they could not growat 37°C. They also grew in NaNO_3 or Na_2SO_4 medium under the existence of K-, Mg-, and Ca-salt. Na^+ was indispensable for their growth, and it could not be replaced with any other cations. They specially required Na^+ and the other salts in sea water contrasting with other types of bacteria. In other words, the sea water has a role of nutritional supply rather than that of osmotic regulation on the growth of Marine type bacteria. 7. Of 275 strains isolated from sea water in the northern part of the North Pacific and the Bering Sea, about 32 per centwere Marine type, about 50 per cent were Terrestrial type, and about 18 per cent were Halophilic type. It had been known that approximately 95 per cent of the bacteria occurring in the sea are Gram-negative. Most bacteria of Gram-negative flagellate rods belonged to the Marine type. 8. Although organisms belonging to these three groups have been found widely in the sea, the author believes that only the Marine type bacteria in three types should be designated "marine bacteria" in the strict sense. And other types of bacteria which occurred there were in the main composed of the survivors of the continental flora. The V. parahaemolyticus also did not be long to marine bacteria. 9. True marine bacteria could best be distinguished from land contaminants present in sea water by their growth capacity manifested in the five types of defined media established. 10. The Marine type bacteria were shown to require a relatively high concentration of Na^+ for their optimal growth and metabolic activity, and also other inorganic salts such as K-, Mg-, and Ca- salt in sea water for their growth. In the investigation on the effects of NaCl and these other inorganic salts on the metabolism of intact cells of Marine type bacteria, it was revealed that NaCl had a specific, positive effect on their enzymic systems, while the other salts had cytological effects on their cell structure, particularly on the structure of cell walls, rather than the effect on their metabolic activity